Browsing by Author "Hsu, C. H."

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A compact biological cell irradiation system with a Van de Graaff accelerator
(2013-11-15)
Cho, I. C.
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Niu, H.
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Chen, C. H.
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Chou, W. T.
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Yu, Y. C.
This report describes the development of a compact microcell irradiation system in the 3 MV MN Van de Graaff accelerator in the Accelerator Laboratory of National Tsing Hua University (NTHU). The main feature of this system is backscattering, a technique whereby a 100 nm gold scattering foil is placed in the center of a scattering chamber, instead of a 90 bending magnet. The incident particles produced by the accelerator bombard the scattering foil and scatter isotropically. A set of micro pinholes was installed above the scattering foil and directed the 90 scattering particles to irradiate the cell target. This innovation simplifies the system design and massively reduces the cost and space requirements for system construction. (C) 2013 Elsevier B.V. All rights reserved.
A Novel Cell Irradiation System Using 90 degrees-Scattering Technique
(2011-02-01)
Cho, I. C.
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Weng, M. F.
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Wu, J. M.
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Chiang, S. Y.
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Chou, W. T.
A novel cell irradiation system was developed for use with the HVEE Van de Graaff accelerator at the National Tsing Hua University. A 90 degrees-scattering technique using an Au foil was designed, in which charged particles were directed from horizontal to vertical irradiation. Beam performance was tested with a silicon detector and a CR-39 nuclear track detector. The HeLa cells were irradiated with 2-MeV alpha particles and the formation of giant cells was observed. The result showed that this system provides a convenient way of generating a vertical particle beam and a cell-supporting chamber, thereby allowing a suitable cell growth condition during irradiation. Furthermore, establishment of such a system is more convenient and economical than the alternatives.
A Novel Cell Irradiation System Using Backscattering Technique
(2009-01-01)
Cho, I. C.
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Chen, C. H.
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Weng, M. F.
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Chiang, S. Y.
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Chou, W. T.
In this paper, we report a novel cell irradiation system at the HVEE Van de Graaff accelerator at National Tsing Hua University. The significant change of system design is use the backscattering technique to replace the 900 magnet which was widely used to derive beam direction from horizontal to vertical. A silicon barrier detector was used to measure the scattered particle energy. Meanwhile, nuclear track detector CR-39 was also applying in this study to assess the particle distribution at beam nozzle. The preliminary experiment performed by using 2 MeV alpha particle to irradiate the HeLa cell. The result showed, this system can provide an efficiently vertical particle beam irradiation and a standard growth condition during the period of irradiation. Furthermore, it's more economical and easier to set up than others.
A Vocoder for a Novel Cochlear Implant Stimulating Strategy Based on Virtual Channel Technology
(2009)
Choi, Charles T. M.
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Hsu, C. H.
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Tsai, W. Y.
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Lee, Yi Hsuan
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資訊工程學系
Cochlear implant provides opportunity for profoundly hearing impairment patient to have a chance to hear sound again. However, the limited number of electrodes is in sufficient to provide enough hearing resolution for hearing impaired people, especially for application in tonal language and music. Virtual channel technology opens up the possibility to increase the hearing resolution under the limited electrodes available and improve and quality for tonal language and music. In this paper, vocoder implementation of a new speech strategy based on virtual channel technology is used to study the improvement. The test result shows improved understanding and quality with virtual channels over the traditional strategies, ex. CIS, especially for mandarin and music.
Control of metamorphic buffer structure and device performance of InxGa1-xAs epitaxial layers fabricated by metal organic chemical vapor deposition
(2014-12-05)
Nguyen, H. Q.
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Yu, H. W.
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Luc, Q. H.
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Tang, Y. Z.
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Phan, V. T. H.
Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique\'s precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (similar to 10(6)cm(-2)), while keeping each individual SG layer slightly exceeding the critical thickness (similar to 80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 mu m. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 x 10(12) eV(-1) cm(-2) in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.
DNA double-strand breaks induced along the trajectory of particles
(2011-12-15)
Cho, I. C.
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Niu, H.
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Chen, C. H.
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Yu, Y. C.
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Hsu, C. H.
It is well-known that the DNA damage caused by charged particles considerably differs from damage due to electromagnetic radiation. In the case of irradiation by charged particles the DNA lesions are more complex and clustered. Such clustered damage is presumed difficult to be repaired, and is potentially lethal. In this study, we utilize a 90 degrees-scattering system and related imaging techniques to investigate the accumulation of gamma-H2AX along the trajectory of charged particles. By immunostaining the gamma-H2AX protein, optical images of corresponding double strand breaks were observed using a high resolution confocal microscope. We demonstrate the difference in the accumulation of gamma-H2AX from irradiation by 1 MeV protons and that of 150 key X-rays. The acquired images were arranged and reconstructed into a 3D image using ImageJ software. We discovered that the gamma-H2AX foci, following irradiation by protons, have a tendency to extend in the beam direction, while those from X-ray irradiation tend to be smaller and more randomly distributed. These results can be explained by the physical model of energy deposition. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.
Enhanced spectral response by silicon nitride index matching layer in amorphous silicon thin-film solar cells
(2012-09-01)
Hsu, C. H.
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Lin, Y. P.
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Hsu, H. J.
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Tsai, C. C.
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光電工程學系
We employed the low temperature hydrogenated amorphous silicon nitride (a-SiNx:H) prepared by plasma-enhanced chemical vapor deposition as a refractive index (n) matching layers in a silicon-based thin-film solar cell between glass (n = 1.5) and the transparent conducting oxide (n = 2). By varying the stoichiometry, refractive index and thickness of the a-SiNx:H layers, we enhanced the spectral response and efficiency of the hydrogenated amorphous silicon thin-film solar cells. The refractive index of a-SiNx:H was reduced from 2.32 to 1.78. Optimizing the a-SiNx:H thickness to 80 nm increased the J(SC) from 8.3 to 9.8 mA/cm(2) and the corresponding cell efficiency increased from 4.5 to 53%, as compared to the cell without the a-SiNx:H index-matching layer on planar substrate. The a-SiNx:H layers with graded refractive indices were effective for enhancing the cell performance. (C) 2012 Elsevier B.V. All rights reserved.
Extreme Hyperlactatemia After Heart Transplantation: One Center's Experience
(2015-07-01)
Hsu, Y. C.
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Hsu, C. H.
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Huang, G. S.
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Lu, C. C.
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Wu, Z. F.
Introduction. Hyperlactatemia may occur early after cardiac surgery and is correlated with prognosis. This study was conducted to analyze the perioperative variables and postoperative outcomes among heart transplant recipients with extremely high lactate levels (>15 mmol/L). Methods. The single-center medical records of heart transplantation from June 2006 to May 2013 were retrospectively reviewed for patient characteristics, perioperative hemodynamic variables, arterial blood gas analysis data, and postoperative mortality. Results. Among 58 consecutive heart transplant recipients, lactate levels over the detectable upper limit (>15 mmol/L) were identified in 12 patients after intensive care unit admission, with peak time at 1.9 +/- 2.0 (range 0-6.1) hours. The maximal preoperative lactate level was 3.1 mmol/L, and most (11/12) postoperative lactate levels returned to <4 mmol/L at 27.5 +/- 12.8 hours after surgery (range 15-58, median 24), displaying a trend toward delayed extubation time in 10 recipients (P < .01). Blood glucose levels elevated significantly from preoperative 148.9 +/- 45.2 to 375.7 +/- 96.9 mg/dL at peak lactate level (P < .01). Four patients died in the ICU (range 5-32 days), 4 died after discharge (range 5-57 months), with 6 in total surviving over 1 year. Conclusion. Extreme hyperlactatemia commonly occurred early after heart transplantation and mostly recovered within 30 hours; however, with delayed extubation time after operation.
Field emission characteristics of chromium carbide capped carbon nanotips
(2006-11-25)
Hsu, C. H.
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Chen, C. F.
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Lo, H. C.
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材料科學與工程學系
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Department of Materials Science and Engineering
In this study, field emission characteristics of two carbon based nanomaterials, carbon nanotips and chromium carbide capped carbon nanotips, were discussed. Both of these materials were synthesized by bias-assisted microwave plasma chemical vapor deposition with hydrogen and methane as reactants. Ultra-sharpness of the carbon nanotips and the composite structure of chromium carbide capped carbon nanotips have shown unique structural and electrical properties. I-V measurements were carried out to investigate the field emission characteristics. The chromium carbide capped carbon nanotips showed superior field emission stability compared to carbon nanotips under constant current emission. (c) 2006 Elsevier B.V. All rights reserved.
Green emitting polyhedral oligomeric silsesquioxanes/poly(phenylene vinylene) derivative materials for highly efficient organic light emitting diodes (OLEDs)
(2008-06-01)
Lee, C. W.
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Josse, Y.
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Hsu, C. H.
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Nguyen, T. P.
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應用化學系
Hybrid materials composed of polyhedral oligomeric silsesquioxanes (POSS) and a polyphenylene vinylene (PPV) derivative were fabricated and characterized by optical and surface spectroscopy. The hybrid thin films have similar optical properties as the pristine polymer but contributions of the POSS are evidenced in infrared spectroscopy. Organic light emitting diodes using the hybrid material as an emitter clearly showed an improvement of the electrical characteristics and the efficiency of the devices as compared to those using the pristine polymer. The effects of POSS incorporation to the polymer are discussed via the obtained results.
Growth and structural characteristics of GaN/AlN/nanothick gamma-Al(2)O(3)/Si (111)
(2008-05-01)
Lee, W. C.
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Lee, Y. J.
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Tung, L. T.
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Wu, S. Y.
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Lee, C. H.
The authors report on the growth of GaN by nitrogen plasma-assisted molecular beam epitaxy (MBE) on a 2 in. Si (111) substrates with a nanothick (similar to 4.8 nm thick) gamma-Al(2)O(3) as a template/buffer. A thin layer of MBE-AlN similar to 40 nm thick was inserted prior to the growth of GaN. High-resolution transmission electron microscopy (HR-TEM) and high-resolution x-ray diffraction studies indicated that both of the nanothick gamma-Al(2)O(3) and AlN are a single crystal. Reflection high-energy electron diffraction, high-resolution x-ray scattering using synchrotron radiation, and cross-sectional HR-TEM measurements indicated an orientation relationship of GaN(0002)parallel to AlN(0002)parallel to gamma-Al(2)O(3)(111)parallel to Si(111) and GaN[10-10]parallel to AlN[10-10]parallel to gamma-Al(2)O(3)[2-1-1]parallel to Si[2-1-1]. A dislocation density of 5x(10(8)-10(9))/cm(2) in the GaN similar to 0.5 mu m thick was determined using cross-sectional TEM images under weak-beam dark-field conditions. (C) 2008 American Vacuum Society.
Growth of optical-quality, uniform In-rich InGaN films using two-heater metal-organic chemical vapor deposition
(2013-11-15)
Fu, S. F.
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Chen, C. Y.
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Li, F. W.
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Hsu, C. H.
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Chou, W. C.
Good-optical-quality, thick InxGa1-xN films with high In content were grown using a homemade two-heater metal-organic chemical vapor deposition system. By varying the growth temperature, it was Found that the In composition of the InGaN epilayer varied from 18 to 59% as the substrate temperature decreased from 750 to 625 degrees C. Our results show that the optical properties in terms of the emission peak wavelength and linewidth are uniformly distributed throughout the entire 2 in. wafer for the x=0.40 InGaN sample. The resultant mean peak wavelength and FWHM are 808 +/- 6 nm and 229 +/- 18 meV, respectively, at 18 K. In addition, for the InGaN film grown at 625 degrees C, a noticeable decrease in the In composition occurred when the ceiling temperature was >800 degrees C, indicative of the occurrence of parasitic reactions in the gas phase. (C) 2013 Elsevier B.V. All rights reserved.
In0.5Ga0.5As-Based Metal-Oxide-Semiconductor Capacitor on GaAs Substrate Using Metal-Organic Chemical Vapor Deposition
(2013-01-01)
Nguyen, H. Q.
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Trinh, H. D.
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Chang, E. Y.
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Lee, C. T.
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Wang, Shin Yuan
We demonstrate the good-performance In0.5Ga0.5As-based metal-oxide-semiconductor capacitor (MOSCAP) on GaAs substrate using metal-organic chemical vapor deposition technique. In0.5Ga0.5As film grown on GaAs substrate is proved to be high quality with threading dislocation density as low as 10(6) cm(-2). The performance of the MOSCAPs is comparable to that of In0.53Ga0.47As/InP-based devices grown by molecular beam epitaxy technique. The devices show a nice capacitance-voltage response, with small frequency dispersion. The parallel conductance contours show the free movement of Fermi level with the gate bias. Acceptable interface trap density D-it values of 5 x 10(11)-2 x 10(12) eV(-1) . cm(-2) in the energy range of 0.64-0.52 eV above the InGaAs valence band maximum in In0.5Ga0.5As/GaAs MOSCAPs obtained by conductance methods were shown.
Influence of Hydrogen on the Germanium Incorporation in a-Si1-xGex:H for Thin-Film Solar Cell Application
(2010-01-01)
Wang, C. M.
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Huang, Y. T.
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Yen, K. H.
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Hsu, H. J.
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Hsu, C. H.
In this work, we examined the Ge incorporation and the accompanied defect formation during PECVD deposition of hydrogenated amorphous silicon-germanium alloys (a-Si1-xGex:H). In particular, we studied the effect of hydrogen on film growth, defect formation, Ge and Si incorporation efficiencies, and the H-bonding configuration. Our results indicate that hydrogen has a strong effect on improving the a-Si1-xGex:H film quality and the Ge incorporation in a-Si1-xGex:H. With adequate hydrogen dilution, the a-Si1-xGex:H thin-film quality significantly improved. However, excessive hydrogen dilution degraded the film properties. A number of analytical tools were employed, including FTIR, XPS, UV-Visible spectroscopy, photoconductivity, etc. The a-Si1-xGex:H material having 24% Ge content and a bangap of 1.61ev produced the solar cell with a conversion efficiency of 7.07%.
Magnetotransport properties, electronic structure, and microstructure of La0.7Sn0.3MnO3 thin films
(2006-10-01)
Cheng, T. Y.
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Lin, C. W.
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Chang, L.
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Hsu, C. H.
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Lee, J. M.
Single-phase La0.7Sn0.3MnO3 (LSnMO) thin films were fabricated on LaAlO3 (LAO) substrates by pulsed laser deposition (PLD). The as-deposited films, though showed insulating characteristics with no sign of insulator-metal transition (IMT) down to very low temperatures, did display a paramagnetic-ferromagnetic transition (PFT) around 180 K. The x-ray absorption spectroscopy (XAS) of the as-deposited LSnMO films shows signature of Mn3+/Mn2+ mixed valence indicating that tetravalent Sn ions may have resulted in electron doping into the e(g) band of Mn. The transmission electron microscopy (TEM) analyses on the as-deposited LSnMO films further confirmed that the films are epitaxial with uniform composition distributions. It is suggestive that the doping level of x=0.3 in La1-xSnxMnO3 can be achieved without disrupting the perovskite structure or any composition inhomogeneity. On the other hand, ex situ annealing in oxygen as well as in argon atmosphere, though both drive the films to display IMT and a marked enhancement in the transition temperature, the preservation of LSnMO phase is somewhat doubtful. In the oxygen-annealing case, the evidence from the XAS measurements on Sn ions though showed the existence of tetravalent characteristics, the Hall measurements indicated that the obtained LSnMO films are p type in nature. Furthermore, the TEM analyses also revealed the emergence of the Sn compounds, which may ultimately drive the obtained films into La-deficient La1-xMnO3 phases.
MBE-Enabling technology beyond Si CMOS
(2011-05-15)
Chang, P.
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Lee, W. C.
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Lin, T. D.
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Hsu, C. H.
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Kwo, J.
Achievement of low interfacial densities of states, small equivalent oxide thickness, high kappa values, and thermal stability at high temperatures in the high kappa dielectrics on high carrier mobility semiconductors, the leading candidates for technology beyond Si CMOS, has been made using MBE. This paper reviews our recent advances in meeting the unprecedented demands in materials and physics for the new technology. Moreover, self-aligned inversion-channel InGaAs and Ge MOSFETs using MBE-Ga(2)O(3)(Gd(2)O(3)) as the gate dielectric are compared favorably with those using the gate dielectrics made from other thin film techniques. (C) 2010 Elsevier B.V. All rights reserved.
Optimal production run time for two-stage production system with imperfect processes and allowable shortages
(2011-12-01)
Pearn, W. L.
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Su, R. H.
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Weng, M. W.
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Hsu, C. H.
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工業工程與管理學系
This paper considers a two-stage production system with imperfect processes. Shortages are allowed, and the unsatisfied demand is completely backlogged. In addition, the capital investment in process quality improvement is adopted. Under these assumptions, we first formulate the proposed problem as a cost minimization model where the production run time and process quality are decision variables. Then we develop the criterion for judging whether the optimal solution not only exists but also is unique. If the criterion is not satisfied, the production system should not be opened. An algorithm for the computations of the optimal solutions is also provided. Finally, a numerical example and sensitivity analysis are carried out to illustrate the model.
Optimization of the absorber layer for a-Si:H and a-Si1-xGex:H single-junction solar cells
(2011)
Tsai, C. C.
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Hsu, C. H.
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Hsu, H. J.
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Cheng, P. H.
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Wang, C. M.
This paper focuses on the optimization of the absorber layers in single-junction a-Si:H and a-Si1-xGex:H solar cells. For a-Si:H thin-film solar cells, we have found the electrode-to-substrate (E/S) spacing is an important parameter. By optimizing the E/S spacing, the cell effi-ciency was improved from 7.62% to 8.70% due to an improvement in material quality and JSC. For a-Si1-xGex:H solar cells, by optimizing the Ge-content, the microstructure parameter and the graded bandgap, we were able to improve the cell efficiency to 8.15%. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Structural distortion and electronic states of Rb doped WO3 by X-ray absorption spectroscopy
(2016-01-01)
Wang, Y. C.
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Hsu, C. H.
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Hsu, Y. Y.
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Chang, C. C.
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Dong, C. L.
Rubidium tungsten bronzes (RbxWO3) have recently attracted much attention due to their intriguing phenomena, such as complex structural phase transitions, strong electron-phonon coupling, and superconducting properties. This study investigates the local atomic and electronic structures of RbxWO3 (0.17 <= x <= 0.33). X-ray powder diffraction patterns showed a hexagonal tungsten bronze (HTB) phase. X-ray absorption spectra (XAS) at the W L-3-edge and Rb K-edge of RbxWO3 were carried out. The XAS analysis indicated a local distorted WO6 octahedron which leads to a splitting of e(g) and t(2g) energy states in the tungsten 5d orbital and this splitting of energy levels exhibited an asymmetrical behavior at x = 0.23 and 0.27. Overall analysis revealed a distortion of local atomic structure of the WO6 octahedra by rubidium doping, leading to the modification of the electronic structures of e(g) and t(2g) states in the tungsten 5d orbital, thereby accounting for the property changes in CDW formation and superconducting transition temperature of these materials.
Study of Crystallinity in mu c-Si: H Films Deposited by Cat-CVD for Thin Film Solar Cell Applications
(2010-01-01)
Hsu, C. H.
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Hsu, Y. P.
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Yao, F. H.
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Huang, Y. T.
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Tsai, C. C.
The crystallinity of the hydrogenated microcrystalline silicon (mu c-Si:H) film was known to influence the solar cell efficiency greatly. Also hydrogen was found to play a critical role in controlling the crystallinity. Instead of employing conventional plasma deposition techniques, this work focused on using catalytic chemical vapor deposition (Cat-CVD) to study the effect of hydrogen dilution and the filament-to-substrate distance on the crystallinity, deposition rate, microstructure factor and electrical property of the mu c-Si: H film. We found that the substrate material and structure can affect the crystallinity of the mu c-Si: H film and the incubation effect. Comparing bare glass, TCO-coated glass, a-Si: H-coated glass and mu c-Si: H-coated glass, the microcrystalline phase grows the fastest onto mu c-Si: H surface, but the slowest onto a-Si: H surface. Surprisingly, the template effect lasted for more than a thousand atomic layers of silicon.